A roller bearing can utilize a cage with multiple parts that are fastened with swaged fasteners to retain the rollers in the cage. In the locomotive industry, a known roller bearing utilizing swaged fasteners for a cage has a “pitch” diameter of about 10 inches. The “pitch” diameter of the bearing is generally two times a distance between the centerline of the rollers with respect to a rotational axis of the bearing. The known roller bearing has a two-piece cage to retain a plurality of rollers between outer and inner races. The cage has an annular cover and an annular base with projecting fingers arranged in an equiangular array about the rotational axis. Each swaged fastener can secure the annular cover to the annular base of the cage by initially mounting a shank portion of the fastener through apertures formed through the cover and base of the cage. A force, i.e., a preload, to ensure that the cage cover and base are fixed to each other is applied through the shank of the fasteners with a suitable tool. While the preload is being applied to the bolt having a shank of a fastener, a collar is swaged to the bolt, thereby allowing the fastener (e.g., bolt and collar) to retain the cage cover and base together via the force of the preload. When the known roller bearing is fully assembled, the fasteners permit the bearing to transmit loads and to maintain a fixed spatial relationship between the cage, races and rollers in the operational environment of a locomotive.
Such operational environment can be demanding on the ability of the bearing to carry a load for a suitable service life. Generally, the known bearing is configured to withstand an operating environment where a shock loading is on the order of 10–15 Gs (i.e., 1 G being an acceleration constant), cage accelerations up to 2000 rpm/sec and bearing resonant frequencies above 70H and is predicted to have an useful service life of as long as a million miles. That same bearing—operating under adverse operating conditions—may not fulfill the predicted service life of a million miles and could be of much lower duration. For example, the known bearing under adverse operating conditions, such as, repeated shock loads of approximately 80 Gs, may have a useful service life of 300,000 miles or less.
It is believed that bearing performance degradation under the increased shock loading may be evident in the proximity of the cage fastener. More particularly, the fastener apertures in the open cage may become enlarged thereby causing misalignment of the bearing components and, in particular, separation of the components of the cage. It has been found that the known bearing arrangement may experience failure, which is believed to be the result of the change in the spatial relationship between cage geometry and fastener geometry while operating under extreme or adverse conditions. In particular, the known bearing has a nominal diameter about the central axis of the bearing to the rotational axis of the cylindrical roller bearing (the pitch circle diameter) of approximately ten inches (10 in.). The known bearing has a two-piece cage with a fastener that includes a bolt and a collar. The bolt has a shank with a nominal shank diameter of 3/16 inches, a final length (measured from the inside of the bolt head to the outside of the collar) of approximately 3.4 inches with a surface arranged to engage a portion of the cage. The surface of the shank has a diameter of approximately 0.329 inches. The collar has a diameter of approximately 0.300 inches and includes a surface that engages another portion of the cage. Each of the surfaces that engages the respective portion of the cage provides an effective area in which the head or collar applies a retention force to the cage. The effective area of the known fastener may be calculated by evaluating the total surface area of the fastener that engages the cage. For example, the respective surface of the bolt head and collar that engages the cage less the surface area of the aperture in which a shank of the fastener is disposed therein. The effective areas of the known bolt head and collar are therefore approximately 0.048 in.2 and 0.042 in.2, respectively. Under adverse operating conditions, the known fastener with these effective areas has been-found to be unable to retain the cage for a suitable service life.
It is recognized engineering practice that, in order to provide sufficient clamping force to components in which the fastener is unable to secure the components together, a possible solution is to increase the size of the bolt head or the collar. Such solution, however, may not be suitable depending on the operational or physical constraints specific to the fastener or the application in which the fastener is being used therein. Thus, the application of this engineering practice is specific to the particular fastening arrangement and the inclination to apply this solution may not be applicable to fasteners in roller bearing cage—where the fasteners have been inadequate in retaining the cage under adverse operating conditions—once all the components, including the fasteners, of the roller bearing have been evaluated.
In the case of the known bearings, individuals specializing in the fastener art have recommended, upon evaluation of the performance of the fastening arrangement in the known roller bearing in which the fasteners have been inadequate in retaining the cage under adverse operating conditions, that an increased preload to the fasteners would be required to secure the components of the cage together. To ensure that the fastener is able to withstand the recommended increase in preload, these individuals have indicated that the nominal size of the shank of the fastener would have to be increased, nominally, from 3/16 to ¼ inches. These individuals have also indicated that an increase in the effective surface areas of the fastener would be required to reduce stress concentration on the cage surfaces. The recommended increase in the preload would also necessitate a larger bolt head than those of the known fasteners. Consequently, the fastener apertures in the cage would also have to be enlarged to accommodate the larger shank of such a bolt (i.e., ¼ inch nominal diameter shank) and the known cage configuration may have to be altered, modified or redesigned to allow a collar to be swaged to the shank. These changes to the cage could affect the performance of the cage, which may require a roller bearing incorporating these changes in the cage to undergo testing and re-certification before being placed into operational service.
Therefore, it would be desirable to provide for a solution to the problem of cage separation while utilizing the existing cage and roller arrangement.